1. Field Of The Invention
This invention pertains to resistor networks and particularly to improvements in crosstalk characteristics of resistor networks.
2. Description Of The Related Art
The application of smaller geometries and higher operating frequencies in electronic circuitry results in undesirable crosstalk between neighboring components. Resistor networks which have resistors grouped together on a common substrate have had a significant problem with high frequency crosstalk. To reduce crosstalk, manufacturers of resistor networks have incorporated discrete capacitors into the resistor network in order to lower the crosstalk between adjacent resistors. This is illustrated in U.S. Pat. No. 4,626,804 to Risher et al. The discrete capacitors lower crosstalk by coupling signals which might otherwise produce crosstalk to ground, thereby attenuating the undesirable signal. R/C networks have only been used in those applications which would be detrimentally affected by crosstalk because the cost of adding the discrete capacitor is substantial.
The provision of a discrete capacitor is expensive for several reasons. The manufacturer of resistor networks is seldom also the manufacturer of discrete capacitors and must incur extra materials expense acquiring capacitors. The handling of discrete capacitors is very different from standard screen printing operations and thereby adds to manufacturing expense. The discrete capacitor has dimensions which are very different from screen printed conductors and resistors and therefore requires special substrates or larger dimensions for inclusion in the network. Each of these complications adds to the expense of the network, which in turn limits applications and reduces sales of R/C networks. Lowered sales means lowered production volume thereby increasing expense further. Because of these disadvantages, manufacturers have avoided the inclusion of capacitors with resistor networks in every possible instance.
In order to overcome the limitations imposed by discrete capacitors, manufacturers have considered several options. The first is to screen print a capacitor. However, screen printed dielectrics are unusual and more costly. The extra printing and firing steps required to print the conductive for the capacitor, then the dielectric, and then the top conductive directly increases cost through additional processing steps and indirectly increases cost by lowering yield. The amount of capacitance of the screen printed capacitor is difficult to control, since screen printing thicknesses are far from precise and the resulting dielectric may be of widely varying thickness. Trimming of a screen printed capacitor is not as rapid or simple an operation as trimming a resistor. There are three layers which will be affected as opposed to one, and the electronics necessary to control the trimming operation is more complicated and generally slower. Each of these factors contribute to making the use of thick film screen printed capacitors undesirable.
Where large values of capacitance are not needed, Kodama in U.S. Pat. No. 2,665,376 teaches the use of screen printed capacitors using the substrate as the dielectric and distributed capacitive shields to reduce intercapacitive coupling between capacitors in a capacitive network. This is disclosed in reference to a capacitor network.
Additional examples of distributed capacitors in combination with resistors are provided by Wasyluk in U.S. Pat. No. 3,402,372 and Bourgault et al in U.S. Pat. No. 3,273,027.